Patent Literature 1 listed below describes that air conduction sound and bone conduction sound are known as sound that is transmitted from an electronic device such as a mobile phone to a human being. It is also described that air conduction sound is sound perceived by an auditory nerve of a user as a result of an eardrum being vibrated by an air vibration that is created by a vibration of an object and that travels through an external auditory canal down to the eardrum. Furthermore, it is described that bone conduction sound is transmitted to the auditory nerve of the user through a part of a user's body (e.g. a cartilaginous portion of an external ear) that is in contact with the vibrating object.
Patent Literature 1 also describes that, in a mobile phone that transmits sound to the user by air conduction sound and bone conduction sound, a rectangular plate-shaped vibration body configured by piezoelectric bimorph and a flexible material is attached to an outer surface of a housing via an elastic member. It is also described that upon application of a voltage to the piezoelectric bimorph of the vibration body, the piezoelectric bimorph is expanded and contracted in a longitudinal direction, thereby vibrating the vibration body. Furthermore, it is described that, when the user places the vibration body in contact with an auricle, air conduction sound and bone conduction sound are transmitted to the user.